[roll third_party/pigweed] pw_string: Reenable insert, erase tests

This CL re-enables tests for insert and erase that were disabled while
debugging CQ failures in pwrev/148333.

These tests push the qemu_gcc version of string_test over the same flash
size threshold that the qemu_clang version crossed some months ago. In
particular, the qemu_gcc_debug version no longer fits into lm3s6965evb's
flash size of 255 KiB. The qemu_clang workaround of only building the
"size_optimized" version of string_test for that target has been applied
to qemu_gcc as well.

Original-Bug: b/244604080
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/149434

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: ce3e1280fcac046..7c875693d478ac0
Roller-URL: https://ci.chromium.org/b/8779285629919075361
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I777de7625d5910092a26da0d39a882ee5512be8c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/150531
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index ce3e128..7c87569 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ce3e1280fcac0461258874eea3e917f6b30be573
+Subproject commit 7c875693d478ac0da2f358a1542a4fc1cad1b60d